TOC component removing apparatus and process for removing TOC components

ABSTRACT

A TOC component removing apparatus removes TOC components contained in ultrapure water or pure water. The apparatus includes a treatment tank into which the ultrapure water or the pure water is introduced, a plurality of spherical catalyst particles of which surfaces are photocatalyst, a tabular translucent holding body which holds the catalyst particles on one surface, and an ultraviolet-ray light source which is arranged near the translucent holding body and radiates ultraviolet rays with a wavelength of 254 nm.

This application is a divisional of application Ser. No. 11/181,896filed Jul. 15, 2005, which in turn claims priority of Japaneseapplication Ser. No. 2004-211339 filed Jul. 20, 2004, the entirecontents of each of which is incorporated by reference in thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for removing TOC componentsand an apparatus for removing TOC components which are contained in aliquid, and relates to technology of removing TOC components containedin liquid, such as ultrapure water used in a process for producing asemiconductor, a liquid crystal, or medical supplies.

Priority is claimed on Japanese Patent Application No. 2004-211339,filed Jul. 20, 2004, the content of which is incorporated herein byreference.

2. Description of Related Art

With technological innovation and advance of technology in recent years,in the semiconductor industry, the liquid crystal industry, and thepharmaceutical industry, etc., ultrapure water (pure water) from whichTOC components, such as organic matter, pyrogen, and bacteria, not tomention dissolved substances and suspended granular materials, such asions, are removed as much as possible, is required. Such ultrapure wateris produced by an ultrapure water producing system which is constitutedby combining a filtrating apparatus, an ion exchanging apparatus, ahyper filtrating membrane apparatus, and a reverse osmosis membraneapparatus, etc., suitably.

However, although this ultrapure water producing system is effective toremove dissolved substances, such as ions and suspended granularmaterials, etc. contained in the unpurified water which is a processingtarget, it is not so effective to remove TOC components, such as organicmaterials, pyrogen, and bacteria, that is, TOC components of 5 to 20 ppbremain in the ultrapure water. If such ultrapure water in which TOCcomponents remain is used in the above fields, there is a possibilitythat various troubles may occur. For example, when ultrapure water inwhich TOC components of 5 to 20 ppb remain is used as a rinsing water inproducing semiconductors, such as LSIs, these TOC components adhere tothe semiconductors as scales to cause contamination of thesemiconductor, circuit destruction, etc. thereby lowering the yield ofproducts.

In order to solve the problem mentioned above, for example, patentdocument 1(Japanese Unexamined Patent Application, First Publication No.10-151450) discloses a method for reducing TOCs by using a lamp whichemits wavelength of 185 nm and 254 nm ultraviolet rays within a purewater tank.

In this method, the oxygen molecules in the tank are changed to ozone byradiating ultraviolet rays with a wavelength of 185 nm within the purewater tank. Furthermore, hydroxyl radicals are generated by radiatingultraviolet rays with a wavelength of 254 nm to the ozone. By the ozoneand the hydroxyl radicals which are generated, the TOCs are oxidized anddecompose to be eliminated.

Moreover, for example, non-patent document 1 (“Water Handbook” WaterHandbook Members-of-Editorial-Board Meeting, Maruzen Co., Ltd., March31, Heisei 15 issue, p. 316-319, p. 345-347) discloses a method ofreducing TOCs using a photocatalyst. In this method, a photocatalyst andan ultraviolet-rays light source are disposed in a pure water tank,whereby ultraviolet rays with a wavelength of 380 nm or less areradiated to the photocatalyst so as to generate hydroxyl radicals on thephotocatalyst surface, thereby oxidizing and decomposing the TOCs to beeliminated.

However, in the method of using ultraviolet rays with wavelength of 185nm and 254 nm, the place in the pure water tank where the ozone and thehydroxyl radicals are generated is not specified, and hence there is apossibility that, when ozone and hydroxyl radicals exist near the rubberpacking in the tank, the rubber sealing is oxidized and decomposes togenerate cracks, thereby causing a leakage of water.

Moreover, in the method of using the photocatalyst, the photocatalyst isa powder which is made of titanium dioxide as the main ingredient, andhence it is used to be carried on the surface of a base material, etc.Since a photocatalyst is a material which is comparatively hard to useas a coat, a binder is mixed when coating. Such a binder is usually anorganic material. Therefore, by receiving ultraviolet rays underwaterfor a long time, hydrolysis may occur, or the binder itself may beoxidized and the binder may be decomposed by the hydroxyl radicalsgenerated on the photocatalyst surface. TOC of the pure water in a purewater tank may increase by decomposition of the binder. Moreover, thebinder decomposes to make the base material unable to hold thephotocatalyst, such that the photocatalyst diffuses and flows out to thepure water path, thereby weakening the oxidizing effect and decomposingeffect of the photocatalyst.

SUMMARY OF THE INVENTION

The present invention was made in view of the above situation. That is,it is an object of the present invention to provide a TOC componentremoving apparatus and a process for removing TOC components, which arecapable of avoiding flowing out of the photocatalyst, and excel in theremoval of TOCs, while preventing degradation of sealing etc., by makinghydroxyl radicals be generated at a specific place.

In order to attain the above object, the present invention adopts thefollowing constitution.

The first aspect of the present invention is a TOC component removingapparatus including: a treatment tank storing untreated ultrapure wateror pure water, a plurality of spherical catalyst particles of which thesurfaces are photocatalyst, a tabular translucent support on a surfaceof which the catalyst particles are distributed and supported, and anultraviolet-rays light source arranged near the translucent supportwhich radiates ultraviolet rays having a wavelength of 254 nm.

According to the above constitution, ultraviolet rays are radiated tocatalyst particles through a translucent support, thereby enablinghydroxyl radicals to be generated only on the surface of the catalystparticles. Although the oxidative effect of hydroxyl radicals ispowerful, lifetime thereof is short, and hence hydroxyl radical existsonly near the catalyst particle surface, and are not widely spread inthe treatment tank, thereby preventing degradation of sealing etc.Moreover, since the catalyst particles are spherical, an area in whichhydroxyl radicals generated can be enlarged, and as a result, ahigh-concentration of hydroxyl radicals can be generated, therebyenabling TOC components to be processed efficiently.

Moreover, since a translucent support is used, there is no possibilitythat the ultraviolet rays may be interrupted. Thereby, the ultravioletrays which are not radiated to catalyst particles can be radiated to theentirety of the treatment tank, whereby it becomes possible to sterilizethe inside of the treatment tank to suppress generation of TOCcomponents.

Moreover, the TOC component removing apparatus of the present inventionmay be a TOC component removing apparatus as mentioned previously, inwhich the catalyst particles are those formed by coating a photocatalystthrough a flame spraying method onto the surface of a spherical carriermade of metal or ceramic.

According to the above constitution, since the photocatalyst is coatedby a flame spraying method, organic ingredients such as a binder, etc.,are not used, thereby preventing increase of the TOC components due todecomposition of the binder.

Moreover, the TOC component removing apparatus of the present inventionmay be the TOC component removing apparatus mentioned above, in whichthe treatment tank has an inner surface which is a mirror surface.

According to the above constitution, the radiated ultraviolet rays arereflected by the inner surface of the treatment tank, therebysterilizing the inside of the treatment tank efficiently.

Moreover, when the ultraviolet rays are radiated to the catalystparticles, portions which become shadowed arise on the catalystparticles, and there is a possibility that photocatalyst action may notdevelop in the shadows, but the reflected ultraviolet rays can beradiated to the shadows by making the inner wall of the treatment tankinto a mirror surface. Thus, according to the above constitution,ultraviolet rays can be radiated all over the surface of the catalystparticles, thereby increasing the removal of the TOC components.

Next, the second aspect of the present invention is a process forremoving TOC components from ultrapure water or pure water, including:introducing untreated ultrapure water or pure water into a treatmenttank, and disposing a plurality of spherical catalyst particles of whichsurface are photocatalyst, a tabular translucent support on a surface ofwhich the catalyst particles are distributed and supported, and anultraviolet-ray light source arranged near the translucent support whichradiates ultraviolet rays having a wavelength of 254 nm within thetreatment tank, and radiating the ultraviolet rays from theultraviolet-ray light source to the catalyst particles, and theultrapure water or the pure water in the treatment tank.

According to the above constitution, ultraviolet rays are radiated tocatalyst particles through a translucent support, thereby enablinghydroxyl radicals to be generated only on the surface of the catalystparticles. Although the oxidative effect of hydroxyl radicals ispowerful, lifetime thereof is short, and hence hydroxyl radical existsonly near the catalyst particle surface, and are not widely spread inthe treatment tank, thereby preventing degradation of sealing etc.Moreover, since the catalyst particles are spherical, an area in whichhydroxyl radicals are generated can be enlarged, and as a result, ahigh-concentration of hydroxyl radicals can be generated, therebyenabling TOC components to be processed efficiently.

Moreover, since a translucent support is used, there is no possibilitythat ultraviolet rays may be interrupted. Thereby, the ultraviolet rayswhich do not radiated the catalyst particles can be radiated to theentirety of the treatment tank, whereby it becomes possible to sterilizethe inside of the treatment tank to suppress generation of the TOCcomponents.

Next, the process for removing TOC components of the present inventionis the process for removing TOC components mentioned above, in which thetreatment tank has an inner surface which is a mirror surface, therebyreflecting the ultraviolet rays to radiate the reflected ultravioletrays to the catalytic particles.

According to the above constitution, the radiated ultraviolet rays arereflected by the inner surface of the treatment tank, therebysterilizing the inside of the treatment tank efficiently.

Moreover, when ultraviolet rays are radiated to the catalyst particles,portions which become shadowed arise on the catalyst particles, andthere is a possibility that photocatalyst action may not develop in theshadows, but the reflected ultraviolet rays can be radiated to theshadows by making the inner wall of the treatment tank into a mirrorsurface. Thus, according to the above constitution, ultraviolet rays canbe radiated all over the surface of the catalyst particles, therebyincreasing the removal of the TOC components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the TOC component removing apparatus of oneembodiment of the present invention.

FIG. 2 is a plan view of the TOC component removing apparatus of oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, one preferred embodiment of the present invention will beexplained while referring to the drawings. The side view of the TOCcomponent removing apparatus of this embodiment is shown in FIG. 1, andthe plan view of the TOC component removing apparatus of this embodimentis shown in FIG. 2.

As shown in FIGS. 1 and 2, the TOC component removing apparatus 1 ofthis embodiment is mainly constituted from a treatment tank 2 into whichuntreated ultrapure water or pure water is introduced, and a pluralityof spherical catalyst particles 3 having surfaces which are made of aphotocatalyst, a tabular translucent support 4 on a surface of which thecatalyst particles 3 are distributed and supported, and anultraviolet-ray light source 5 which is arranged near the translucentsupport 4 and which radiates ultraviolet rays with a wavelength of 254nm.

The treatment tank 2 consists of a tank main body 11, and a tank lid 12which is disposed on the upper part of the tank main body 11. The tankmain body 11 and the tank lid 12 are made of stainless steel, etc., forexample. Moreover, a circulating water flow inlet 11 a, a circulatingwater flow outlet 11 b, and an untreated water feed port 11 c aredisposed on the tank main body 11. Furthermore, mirror surfaceprocessing is performed on the inner wall surface 2 a of the treatmenttank 2 so as to reflect ultraviolet rays therefrom.

Moreover, a circulating mechanism 6 for the ultrapure water or purewater is connected to the tank main body 11. The circulating mechanism 6is constituted from a circulating pump 21, an ion-exchange resin 22, anultra-fine filter 23, a water quality meter 24 for measuring the amountof TOC components, and a three way valve 25 being connected through acirculating path 26. Both ends of the circulating path 26 are connectedto the circulating water flow inlet 11 a and the circulating water flowoutlet 11 b of the tank main body 11, respectively. Moreover, a samplingpath 27 for sampling the treated water circulating from which the TOCcomponents is removed is connected to the three way valve 25.

Moreover, the introducing path (not shown) for introducing untreatedwater before removing TOC components into the tank is connected to theuntreated water feed port 11 c of the tank main body 11.

The catalyst particles 3 are stored inside the treatment tank 2, andcoating of the photocatalyst is carried out by a flame spraying methodonto the surface of a carrier which consists of a spherical metal orceramic.

As the carrier, spherical particles made of stainless steel, aluminaceramic, etc., having a diameter of approximately from not less than 3mm to not more than 6 mm are used. Moreover, as the photocatalyst, thosewhich can generate hydroxyl radicals in response to ultraviolet rayswith a wavelength of 254 nm are employable, for example, which consistof TiO₂, Ag (silver), etc. Moreover, the photocatalyst is preferablycoated on the surface of the carrier at a thickness of approximatelyfrom not less than 30 μm to not more than 70 μm. In order to coat thephotocatalyst onto the carrier, a flame spraying method, which is amethod of fusing a material which constitutes the photocatalyst and thenthrowing the fused material at the carrier at high speed, is preferablyused. It becomes unnecessary to add organic resins, such as a binder, tothe photocatalyst when coating through the flame spraying method.

Next, the translucent support 4 is stored inside the treatment tank 2together with the catalyst particles 3, and consists of a tabular memberwhich transmits ultraviolet rays. The translucent support 4 shown inFIGS. 1 and 2 is mainly constituted from a tabular bottom part 31 and aside wall part 32 disposed upright from the circumference part of thebottom part 31. A plurality of catalyst particles 3 is dispersed overthe whole surface 31 a of the tabular bottom part 31. As for thecatalyst particles 3, it is preferred that the catalyst particles 3 bedisposed leaving a spaces therebetween, such that they may not contacteach other. Moreover, the material of the translucent support 4 may beone which can transmit ultraviolet-rays, and for example, silica glass,soft glass, ultraviolet-ray penetrative acrylics, etc., cay be employed.

Next, the ultraviolet-ray light source 5 which radiates ultraviolet rayswith a wavelength of 254 nm, is disposed onto another surface 31 b ofthe bottom part 31 of the translucent support 4. The ultraviolet raysemitted from the ultraviolet-ray light source 5 are radiated to thecirculating water and the catalyst particles 3 in the treatment tank 2.

Moreover, in the treatment tank 2, two float switches 41 for detectingthe water level in the treatment tank 2 are disposed. The float switch41 a at the bottom of the treatment tank 2 is for detecting drying up ofthe water, whereas the float switch 41 b at the upper part of thetreatment tank 2 is for detecting a high water level.

Next, the process for treating the TOC components in the ultrapure waterusing the above TOC component removing apparatus 1 will be explained.

First, the untreated water which has been passed through a reverseosmosis membrane and an ion-exchange resin is introduced into thetreatment tank 2 from the untreated water feed port 11 a. The untreatedwater is a water from which cations and anions dissolved therein havebeen removed by the ion-exchange resin, while minute suspendedsubstances have been removed by the reverse osmosis membrane. However,TOC components have not been removed.

Next, after the treatment tank is filled with untreated water, supplyingof untreated water is stopped, and the circulating pump 21 is operatedto circulate the untreated water between the treatment tank 2 and thecirculating mechanism 6. At this time, the three way valve 25 is in the“closed” state with respect to the sampling path 27.

Next, ultraviolet rays with a wavelength of 254 nm are generated fromthe ultraviolet-ray light source 5. Some of the generated ultravioletrays permeate the translucent support 4 to be radiated to the catalystparticles 3. The photocatalyst is coated onto the surface of thecatalyst particles 3, and hydroxyl radicals are generated whenultraviolet rays are radiated to this photocatalyst. By the generatedhydroxyl radicals, the untreated underwater TOC components in theuntreated water are oxidized and decomposed.

Moreover, the remaining ultraviolet rays generated from theultraviolet-ray light source 5 are directly radiated to the untreatedwater in the treatment tank 2. Thereby, the untreated water issterilized and increase of the TOC components due to the increase ofbacteria can be prevented beforehand. Moreover, since the translucentsupport 4 shows permeability to ultraviolet rays, ultraviolet rays arenot interrupted by the translucent support 4, and as a result,ultraviolet rays can be radiated to the whole inside of the treatmenttank 2.

Furthermore, since the ultraviolet rays directly radiated to theuntreated water in the treatment tank 2 are reflected by the mirrorinside the treatment tank 2, the sterilizing effect on the untreatedwater can be increased further.

Moreover, on the catalyst particles 3, portions which act as shadows bywhich ultraviolet rays are not radiated directly onto from theultraviolet-ray light source 5 may be formed depending on the spatialrelationship between the catalyst particles 3 and the ultraviolet-raylight source 5. Specifically, in FIG. 1, the upper sides of the catalystparticles 3 become shadows against the ultraviolet-ray light source 5.There is a possibility that the photocatalyst at this portion of theshadows may not be used effectively. However, in the TOC componentremoving apparatus 1 of this embodiment, since the inner wall surface ofthe treatment tank 2 is made to be a mirror surface, such that theultraviolet rays directly radiated to the untreated water are reflectedtherefrom, some of these ultraviolet rays are reflected by the mirrorsurface and are radiated to the portions of the photocatalyst whichbecomes shadowed. Thereby, also at the portions which becomes shadowedagainst the ultraviolet-ray light source 5, hydroxyl radicals can begenerated, and as a result, the concentration of hydroxyl radicals canbe increased, thereby removing TOC components efficiently.

As mentioned above, the TOC components in the untreated water decreasegradually due to performance of ultraviolet-ray irradiationcontinuously, while continuing circulation of the untreated water. Whenthe concentration of the TOC components is less than a predeterminedvalue, the three way valve 25 is operated to make the sample path“open”, and the treated ultrapure water or pure water is sampled. If theamount of circulating water in the treatment tank 2 and the circulatingmechanism 6 decreases, untreated water is supplied again from theuntreated water feed port 11 a.

As explained above, according to the TOC component removing apparatusand the process for removing the TOC components of this embodiment,hydroxyl radicals can be generated only on the surface of the catalystparticles 3, and the TOC components can be decomposed and removed.

Although the oxidative effect of hydroxyl radicals is powerful, lifetimethereof is short, and hence hydroxyl radicals exist only near thecatalyst particles 3 surface, and are not widely spread in the treatmenttank 2, thereby preventing degradation of sealing etc. Moreover, sincethe catalyst particles 3 are spherical, an area in which hydroxylradicals are generated can be enlarged, and as a result, ahigh-concentration of hydroxyl radicals can be generated, therebyenabling the TOC components to be processed efficiently.

Moreover, since a translucent support 4 is used, there is no possibilitythat the ultraviolet rays may be interrupted. Thereby, the ultravioletrays which do not radiated to the catalyst particles 3 can be radiatedto the entirety of the treatment tank 2, whereby it becomes possible tosterilize the inside of the treatment tank 2 to suppress generation ofthe TOC components.

Moreover, according to the above constitution, since the photocatalystis coated by a flame spraying method, organic ingredients such as abinder, etc., are not used, thereby preventing increase of the TOCcomponents due to decomposition of the binder.

In addition, the radiated ultraviolet rays are reflected by the innersurface of the treatment tank 2, thereby sterilizing the inside of thetreatment tank efficiently.

Moreover, when ultraviolet rays are radiated to the catalyst particles3, portions which become shadowed arise on the catalyst particles, andthere is a possibility that photocatalyst action may not develop in theshadows, but the reflected ultraviolet rays can be radiated to theshadows by making the inner wall surface of the treatment tank 2 into amirror surface. By this, ultraviolet rays can be radiated all over thesurface of the catalyst particles 3, thereby increasing the removal ofthe TOC components.

It should be noted that the present invention is not limited to theabove embodiment, and may various changes may be made. For example, itis possible to arrange the position of the ultraviolet-ray light sourcenot only at the lower part of the translucent support but also at theupper part of the translucent support, i.e., above the catalystparticles. Moreover, it is possible to arrange the ultraviolet-ray lightsource and the translucent support equipped with catalyst particles notonly in one treatment tank but in a plurality of places.

As explained above, according to the TOC removing apparatus and theprocess for removing TOC components of the present invention,degradation of sealing, etc., can be prevented by generating hydroxylradicals at a specific place, flowing out of the photocatalyst can beprevented, and the removal of TOCs can be improved further.

The present invention relates to the technology of removing TOCcomponents contained in liquids, such as ultrapure water used in aproduction process for semiconductors, liquid crystal, or medicalsupplies.

1. A process for removing TOC components from ultrapure water or purewater, comprising: introducing untreated ultrapure water or pure waterinto a treatment tank having an inner surface which is a mirror surface,and disposing a plurality of spherical catalyst particles of whichsurfaces are photocatalyst prepared by a flame-spraying method, atabular translucent support on a surface of which the catalyst particlesare distributed and supported, and an ultraviolet-ray light sourcearranged near the translucent support which radiates ultraviolet rayshaving a wavelength of 254 nm within the treatment tank, and radiatingultraviolet rays from the ultraviolet-ray light source to the catalystparticles, and the ultrapure water or the pure water in the treatmenttank.